tools/objtool/check.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
   4  */
   5
   6 #include <string.h>
   7 #include <stdlib.h>
   8
   9 #include "builtin.h"
  10 #include "check.h"
  11 #include "elf.h"
  12 #include "special.h"
  13 #include "arch.h"
  14 #include "warn.h"
  15
  16 #include <linux/hashtable.h>
  17 #include <linux/kernel.h>
  18
  19 #define FAKE_JUMP_OFFSET -1
  20
  21 #define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
  22
  23 struct alternative {
  24         struct list_head list;
  25         struct instruction *insn;
  26         bool skip_orig;
  27 };
  28
  29 const char *objname;
  30 struct cfi_state initial_func_cfi;
  31
  32 struct instruction *find_insn(struct objtool_file *file,
  33                               struct section *sec, unsigned long offset)
  34 {
  35         struct instruction *insn;
  36
  37         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  38                 if (insn->sec == sec && insn->offset == offset)
  39                         return insn;
  40
  41         return NULL;
  42 }
  43
  44 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  45                                               struct instruction *insn)
  46 {
  47         struct instruction *next = list_next_entry(insn, list);
  48
  49         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  50                 return NULL;
  51
  52         return next;
  53 }
  54
  55 static struct instruction *next_insn_same_func(struct objtool_file *file,
  56                                                struct instruction *insn)
  57 {
  58         struct instruction *next = list_next_entry(insn, list);
  59         struct symbol *func = insn->func;
  60
  61         if (!func)
  62                 return NULL;
  63
  64         if (&next->list != &file->insn_list && next->func == func)
  65                 return next;
  66
  67         /* Check if we're already in the subfunction: */
  68         if (func == func->cfunc)
  69                 return NULL;
  70
  71         /* Move to the subfunction: */
  72         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  73 }
  74
  75 #define func_for_each_insn(file, func, insn)                            \
  76         for (insn = find_insn(file, func->sec, func->offset);           \
  77              insn;                                                      \
  78              insn = next_insn_same_func(file, insn))
  79
  80 #define sym_for_each_insn(file, sym, insn)                              \
  81         for (insn = find_insn(file, sym->sec, sym->offset);             \
  82              insn && &insn->list != &file->insn_list &&                 \
  83                 insn->sec == sym->sec &&                                \
  84                 insn->offset < sym->offset + sym->len;                  \
  85              insn = list_next_entry(insn, list))
  86
  87 #define sym_for_each_insn_continue_reverse(file, sym, insn)             \
  88         for (insn = list_prev_entry(insn, list);                        \
  89              &insn->list != &file->insn_list &&                         \
  90                 insn->sec == sym->sec && insn->offset >= sym->offset;   \
  91              insn = list_prev_entry(insn, list))
  92
  93 #define sec_for_each_insn_from(file, insn)                              \
  94         for (; insn; insn = next_insn_same_sec(file, insn))
  95
  96 #define sec_for_each_insn_continue(file, insn)                          \
  97         for (insn = next_insn_same_sec(file, insn); insn;               \
  98              insn = next_insn_same_sec(file, insn))
  99
 100 static bool is_static_jump(struct instruction *insn)
 101 {
 102         return insn->type == INSN_JUMP_CONDITIONAL ||
 103                insn->type == INSN_JUMP_UNCONDITIONAL;
 104 }
 105
 106 static bool is_sibling_call(struct instruction *insn)
 107 {
 108         /* An indirect jump is either a sibling call or a jump to a table. */
 109         if (insn->type == INSN_JUMP_DYNAMIC)
 110                 return list_empty(&insn->alts);
 111
 112         if (!is_static_jump(insn))
 113                 return false;
 114
 115         /* add_jump_destinations() sets insn->call_dest for sibling calls. */
 116         return !!insn->call_dest;
 117 }
 118
 119 /*
 120  * This checks to see if the given function is a "noreturn" function.
 121  *
 122  * For global functions which are outside the scope of this object file, we
 123  * have to keep a manual list of them.
 124  *
 125  * For local functions, we have to detect them manually by simply looking for
 126  * the lack of a return instruction.
 127  */
 128 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 129                                 int recursion)
 130 {
 131         int i;
 132         struct instruction *insn;
 133         bool empty = true;
 134
 135         /*
 136          * Unfortunately these have to be hard coded because the noreturn
 137          * attribute isn't provided in ELF data.
 138          */
 139         static const char * const global_noreturns[] = {
 140                 "__stack_chk_fail",
 141                 "panic",
 142                 "do_exit",
 143                 "do_task_dead",
 144                 "__module_put_and_exit",
 145                 "complete_and_exit",
 146                 "__reiserfs_panic",
 147                 "lbug_with_loc",
 148                 "fortify_panic",
 149                 "usercopy_abort",
 150                 "machine_real_restart",
 151                 "rewind_stack_do_exit",
 152                 "kunit_try_catch_throw",
 153         };
 154
 155         if (!func)
 156                 return false;
 157
 158         if (func->bind == STB_WEAK)
 159                 return false;
 160
 161         if (func->bind == STB_GLOBAL)
 162                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 163                         if (!strcmp(func->name, global_noreturns[i]))
 164                                 return true;
 165
 166         if (!func->len)
 167                 return false;
 168
 169         insn = find_insn(file, func->sec, func->offset);
 170         if (!insn->func)
 171                 return false;
 172
 173         func_for_each_insn(file, func, insn) {
 174                 empty = false;
 175
 176                 if (insn->type == INSN_RETURN)
 177                         return false;
 178         }
 179
 180         if (empty)
 181                 return false;
 182
 183         /*
 184          * A function can have a sibling call instead of a return.  In that
 185          * case, the function's dead-end status depends on whether the target
 186          * of the sibling call returns.
 187          */
 188         func_for_each_insn(file, func, insn) {
 189                 if (is_sibling_call(insn)) {
 190                         struct instruction *dest = insn->jump_dest;
 191
 192                         if (!dest)
 193                                 /* sibling call to another file */
 194                                 return false;
 195
 196                         /* local sibling call */
 197                         if (recursion == 5) {
 198                                 /*
 199                                  * Infinite recursion: two functions have
 200                                  * sibling calls to each other.  This is a very
 201                                  * rare case.  It means they aren't dead ends.
 202                                  */
 203                                 return false;
 204                         }
 205
 206                         return __dead_end_function(file, dest->func, recursion+1);
 207                 }
 208         }
 209
 210         return true;
 211 }
 212
 213 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 214 {
 215         return __dead_end_function(file, func, 0);
 216 }
 217
 218 static void clear_insn_state(struct insn_state *state)
 219 {
 220         int i;
 221
 222         memset(state, 0, sizeof(*state));
 223         state->cfa.base = CFI_UNDEFINED;
 224         for (i = 0; i < CFI_NUM_REGS; i++) {
 225                 state->regs[i].base = CFI_UNDEFINED;
 226                 state->vals[i].base = CFI_UNDEFINED;
 227         }
 228         state->drap_reg = CFI_UNDEFINED;
 229         state->drap_offset = -1;
 230 }
 231
 232 /*
 233  * Call the arch-specific instruction decoder for all the instructions and add
 234  * them to the global instruction list.
 235  */
 236 static int decode_instructions(struct objtool_file *file)
 237 {
 238         struct section *sec;
 239         struct symbol *func;
 240         unsigned long offset;
 241         struct instruction *insn;
 242         unsigned long nr_insns = 0;
 243         int ret;
 244
 245         for_each_sec(file, sec) {
 246
 247                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 248                         continue;
 249
 250                 if (strcmp(sec->name, ".altinstr_replacement") &&
 251                     strcmp(sec->name, ".altinstr_aux") &&
 252                     strncmp(sec->name, ".discard.", 9))
 253                         sec->text = true;
 254
 255                 for (offset = 0; offset < sec->len; offset += insn->len) {
 256                         insn = malloc(sizeof(*insn));
 257                         if (!insn) {
 258                                 WARN("malloc failed");
 259                                 return -1;
 260                         }
 261                         memset(insn, 0, sizeof(*insn));
 262                         INIT_LIST_HEAD(&insn->alts);
 263                         clear_insn_state(&insn->state);
 264
 265                         insn->sec = sec;
 266                         insn->offset = offset;
 267
 268                         ret = arch_decode_instruction(file->elf, sec, offset,
 269                                                       sec->len - offset,
 270                                                       &insn->len, &insn->type,
 271                                                       &insn->immediate,
 272                                                       &insn->stack_op);
 273                         if (ret)
 274                                 goto err;
 275
 276                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 277                         list_add_tail(&insn->list, &file->insn_list);
 278                         nr_insns++;
 279                 }
 280
 281                 list_for_each_entry(func, &sec->symbol_list, list) {
 282                         if (func->type != STT_FUNC || func->alias != func)
 283                                 continue;
 284
 285                         if (!find_insn(file, sec, func->offset)) {
 286                                 WARN("%s(): can't find starting instruction",
 287                                      func->name);
 288                                 return -1;
 289                         }
 290
 291                         sym_for_each_insn(file, func, insn)
 292                                 insn->func = func;
 293                 }
 294         }
 295
 296         if (stats)
 297                 printf("nr_insns: %lu\n", nr_insns);
 298
 299         return 0;
 300
 301 err:
 302         free(insn);
 303         return ret;
 304 }
 305
 306 /*
 307  * Mark "ud2" instructions and manually annotated dead ends.
 308  */
 309 static int add_dead_ends(struct objtool_file *file)
 310 {
 311         struct section *sec;
 312         struct rela *rela;
 313         struct instruction *insn;
 314         bool found;
 315
 316         /*
 317          * By default, "ud2" is a dead end unless otherwise annotated, because
 318          * GCC 7 inserts it for certain divide-by-zero cases.
 319          */
 320         for_each_insn(file, insn)
 321                 if (insn->type == INSN_BUG)
 322                         insn->dead_end = true;
 323
 324         /*
 325          * Check for manually annotated dead ends.
 326          */
 327         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 328         if (!sec)
 329                 goto reachable;
 330
 331         list_for_each_entry(rela, &sec->rela_list, list) {
 332                 if (rela->sym->type != STT_SECTION) {
 333                         WARN("unexpected relocation symbol type in %s", sec->name);
 334                         return -1;
 335                 }
 336                 insn = find_insn(file, rela->sym->sec, rela->addend);
 337                 if (insn)
 338                         insn = list_prev_entry(insn, list);
 339                 else if (rela->addend == rela->sym->sec->len) {
 340                         found = false;
 341                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 342                                 if (insn->sec == rela->sym->sec) {
 343                                         found = true;
 344                                         break;
 345                                 }
 346                         }
 347
 348                         if (!found) {
 349                                 WARN("can't find unreachable insn at %s+0x%x",
 350                                      rela->sym->sec->name, rela->addend);
 351                                 return -1;
 352                         }
 353                 } else {
 354                         WARN("can't find unreachable insn at %s+0x%x",
 355                              rela->sym->sec->name, rela->addend);
 356                         return -1;
 357                 }
 358
 359                 insn->dead_end = true;
 360         }
 361
 362 reachable:
 363         /*
 364          * These manually annotated reachable checks are needed for GCC 4.4,
 365          * where the Linux unreachable() macro isn't supported.  In that case
 366          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 367          * not a dead end.
 368          */
 369         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 370         if (!sec)
 371                 return 0;
 372
 373         list_for_each_entry(rela, &sec->rela_list, list) {
 374                 if (rela->sym->type != STT_SECTION) {
 375                         WARN("unexpected relocation symbol type in %s", sec->name);
 376                         return -1;
 377                 }
 378                 insn = find_insn(file, rela->sym->sec, rela->addend);
 379                 if (insn)
 380                         insn = list_prev_entry(insn, list);
 381                 else if (rela->addend == rela->sym->sec->len) {
 382                         found = false;
 383                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 384                                 if (insn->sec == rela->sym->sec) {
 385                                         found = true;
 386                                         break;
 387                                 }
 388                         }
 389
 390                         if (!found) {
 391                                 WARN("can't find reachable insn at %s+0x%x",
 392                                      rela->sym->sec->name, rela->addend);
 393                                 return -1;
 394                         }
 395                 } else {
 396                         WARN("can't find reachable insn at %s+0x%x",
 397                              rela->sym->sec->name, rela->addend);
 398                         return -1;
 399                 }
 400
 401                 insn->dead_end = false;
 402         }
 403
 404         return 0;
 405 }
 406
 407 /*
 408  * Warnings shouldn't be reported for ignored functions.
 409  */
 410 static void add_ignores(struct objtool_file *file)
 411 {
 412         struct instruction *insn;
 413         struct section *sec;
 414         struct symbol *func;
 415         struct rela *rela;
 416
 417         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 418         if (!sec)
 419                 return;
 420
 421         list_for_each_entry(rela, &sec->rela_list, list) {
 422                 switch (rela->sym->type) {
 423                 case STT_FUNC:
 424                         func = rela->sym;
 425                         break;
 426
 427                 case STT_SECTION:
 428                         func = find_func_by_offset(rela->sym->sec, rela->addend);
 429                         if (!func)
 430                                 continue;
 431                         break;
 432
 433                 default:
 434                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 435                         continue;
 436                 }
 437
 438                 func_for_each_insn(file, func, insn)
 439                         insn->ignore = true;
 440         }
 441 }
 442
 443 /*
 444  * This is a whitelist of functions that is allowed to be called with AC set.
 445  * The list is meant to be minimal and only contains compiler instrumentation
 446  * ABI and a few functions used to implement *_{to,from}_user() functions.
 447  *
 448  * These functions must not directly change AC, but may PUSHF/POPF.
 449  */
 450 static const char *uaccess_safe_builtin[] = {
 451         /* KASAN */
 452         "kasan_report",
 453         "check_memory_region",
 454         /* KASAN out-of-line */
 455         "__asan_loadN_noabort",
 456         "__asan_load1_noabort",
 457         "__asan_load2_noabort",
 458         "__asan_load4_noabort",
 459         "__asan_load8_noabort",
 460         "__asan_load16_noabort",
 461         "__asan_storeN_noabort",
 462         "__asan_store1_noabort",
 463         "__asan_store2_noabort",
 464         "__asan_store4_noabort",
 465         "__asan_store8_noabort",
 466         "__asan_store16_noabort",
 467         /* KASAN in-line */
 468         "__asan_report_load_n_noabort",
 469         "__asan_report_load1_noabort",
 470         "__asan_report_load2_noabort",
 471         "__asan_report_load4_noabort",
 472         "__asan_report_load8_noabort",
 473         "__asan_report_load16_noabort",
 474         "__asan_report_store_n_noabort",
 475         "__asan_report_store1_noabort",
 476         "__asan_report_store2_noabort",
 477         "__asan_report_store4_noabort",
 478         "__asan_report_store8_noabort",
 479         "__asan_report_store16_noabort",
 480         /* KCOV */
 481         "write_comp_data",
 482         "__sanitizer_cov_trace_pc",
 483         "__sanitizer_cov_trace_const_cmp1",
 484         "__sanitizer_cov_trace_const_cmp2",
 485         "__sanitizer_cov_trace_const_cmp4",
 486         "__sanitizer_cov_trace_const_cmp8",
 487         "__sanitizer_cov_trace_cmp1",
 488         "__sanitizer_cov_trace_cmp2",
 489         "__sanitizer_cov_trace_cmp4",
 490         "__sanitizer_cov_trace_cmp8",
 491         "__sanitizer_cov_trace_switch",
 492         /* UBSAN */
 493         "ubsan_type_mismatch_common",
 494         "__ubsan_handle_type_mismatch",
 495         "__ubsan_handle_type_mismatch_v1",
 496         "__ubsan_handle_shift_out_of_bounds",
 497         /* misc */
 498         "csum_partial_copy_generic",
 499         "__memcpy_mcsafe",
 500         "mcsafe_handle_tail",
 501         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 502         NULL
 503 };
 504
 505 static void add_uaccess_safe(struct objtool_file *file)
 506 {
 507         struct symbol *func;
 508         const char **name;
 509
 510         if (!uaccess)
 511                 return;
 512
 513         for (name = uaccess_safe_builtin; *name; name++) {
 514                 func = find_symbol_by_name(file->elf, *name);
 515                 if (!func)
 516                         continue;
 517
 518                 func->uaccess_safe = true;
 519         }
 520 }
 521
 522 /*
 523  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 524  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 525  * But it at least allows objtool to understand the control flow *around* the
 526  * retpoline.
 527  */
 528 static int add_ignore_alternatives(struct objtool_file *file)
 529 {
 530         struct section *sec;
 531         struct rela *rela;
 532         struct instruction *insn;
 533
 534         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 535         if (!sec)
 536                 return 0;
 537
 538         list_for_each_entry(rela, &sec->rela_list, list) {
 539                 if (rela->sym->type != STT_SECTION) {
 540                         WARN("unexpected relocation symbol type in %s", sec->name);
 541                         return -1;
 542                 }
 543
 544                 insn = find_insn(file, rela->sym->sec, rela->addend);
 545                 if (!insn) {
 546                         WARN("bad .discard.ignore_alts entry");
 547                         return -1;
 548                 }
 549
 550                 insn->ignore_alts = true;
 551         }
 552
 553         return 0;
 554 }
 555
 556 /*
 557  * Find the destination instructions for all jumps.
 558  */
 559 static int add_jump_destinations(struct objtool_file *file)
 560 {
 561         struct instruction *insn;
 562         struct rela *rela;
 563         struct section *dest_sec;
 564         unsigned long dest_off;
 565
 566         for_each_insn(file, insn) {
 567                 if (!is_static_jump(insn))
 568                         continue;
 569
 570                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 571                         continue;
 572
 573                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 574                                                insn->offset, insn->len);
 575                 if (!rela) {
 576                         dest_sec = insn->sec;
 577                         dest_off = insn->offset + insn->len + insn->immediate;
 578                 } else if (rela->sym->type == STT_SECTION) {
 579                         dest_sec = rela->sym->sec;
 580                         dest_off = rela->addend + 4;
 581                 } else if (rela->sym->sec->idx) {
 582                         dest_sec = rela->sym->sec;
 583                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 584                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 585                         /*
 586                          * Retpoline jumps are really dynamic jumps in
 587                          * disguise, so convert them accordingly.
 588                          */
 589                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 590                                 insn->type = INSN_JUMP_DYNAMIC;
 591                         else
 592                                 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 593
 594                         insn->retpoline_safe = true;
 595                         continue;
 596                 } else {
 597                         /* external sibling call */
 598                         insn->call_dest = rela->sym;
 599                         continue;
 600                 }
 601
 602                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 603                 if (!insn->jump_dest) {
 604
 605                         /*
 606                          * This is a special case where an alt instruction
 607                          * jumps past the end of the section.  These are
 608                          * handled later in handle_group_alt().
 609                          */
 610                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 611                                 continue;
 612
 613                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 614                                   insn->sec, insn->offset, dest_sec->name,
 615                                   dest_off);
 616                         return -1;
 617                 }
 618
 619                 /*
 620                  * Cross-function jump.
 621                  */
 622                 if (insn->func && insn->jump_dest->func &&
 623                     insn->func != insn->jump_dest->func) {
 624
 625                         /*
 626                          * For GCC 8+, create parent/child links for any cold
 627                          * subfunctions.  This is _mostly_ redundant with a
 628                          * similar initialization in read_symbols().
 629                          *
 630                          * If a function has aliases, we want the *first* such
 631                          * function in the symbol table to be the subfunction's
 632                          * parent.  In that case we overwrite the
 633                          * initialization done in read_symbols().
 634                          *
 635                          * However this code can't completely replace the
 636                          * read_symbols() code because this doesn't detect the
 637                          * case where the parent function's only reference to a
 638                          * subfunction is through a jump table.
 639                          */
 640                         if (!strstr(insn->func->name, ".cold.") &&
 641                             strstr(insn->jump_dest->func->name, ".cold.")) {
 642                                 insn->func->cfunc = insn->jump_dest->func;
 643                                 insn->jump_dest->func->pfunc = insn->func;
 644
 645                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 646                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 647
 648                                 /* internal sibling call */
 649                                 insn->call_dest = insn->jump_dest->func;
 650                         }
 651                 }
 652         }
 653
 654         return 0;
 655 }
 656
 657 /*
 658  * Find the destination instructions for all calls.
 659  */
 660 static int add_call_destinations(struct objtool_file *file)
 661 {
 662         struct instruction *insn;
 663         unsigned long dest_off;
 664         struct rela *rela;
 665
 666         for_each_insn(file, insn) {
 667                 if (insn->type != INSN_CALL)
 668                         continue;
 669
 670                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 671                                                insn->offset, insn->len);
 672                 if (!rela) {
 673                         dest_off = insn->offset + insn->len + insn->immediate;
 674                         insn->call_dest = find_func_by_offset(insn->sec, dest_off);
 675                         if (!insn->call_dest)
 676                                 insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
 677
 678                         if (insn->ignore)
 679                                 continue;
 680
 681                         if (!insn->call_dest) {
 682                                 WARN_FUNC("unsupported intra-function call",
 683                                           insn->sec, insn->offset);
 684                                 if (retpoline)
 685                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 686                                 return -1;
 687                         }
 688
 689                         if (insn->func && insn->call_dest->type != STT_FUNC) {
 690                                 WARN_FUNC("unsupported call to non-function",
 691                                           insn->sec, insn->offset);
 692                                 return -1;
 693                         }
 694
 695                 } else if (rela->sym->type == STT_SECTION) {
 696                         insn->call_dest = find_func_by_offset(rela->sym->sec,
 697                                                               rela->addend+4);
 698                         if (!insn->call_dest) {
 699                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 700                                           insn->sec, insn->offset,
 701                                           rela->sym->sec->name,
 702                                           rela->addend + 4);
 703                                 return -1;
 704                         }
 705                 } else
 706                         insn->call_dest = rela->sym;
 707         }
 708
 709         return 0;
 710 }
 711
 712 /*
 713  * The .alternatives section requires some extra special care, over and above
 714  * what other special sections require:
 715  *
 716  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 717  *    instruction at the end so that validate_branch() skips all the original
 718  *    replaced instructions when validating the new instruction path.
 719  *
 720  * 2. An added wrinkle is that the new instruction length might be zero.  In
 721  *    that case the old instructions are replaced with noops.  We simulate that
 722  *    by creating a fake jump as the only new instruction.
 723  *
 724  * 3. In some cases, the alternative section includes an instruction which
 725  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 726  *    jumps' destinations to point back to .text rather than the end of the
 727  *    entry in .altinstr_replacement.
 728  */
 729 static int handle_group_alt(struct objtool_file *file,
 730                             struct special_alt *special_alt,
 731                             struct instruction *orig_insn,
 732                             struct instruction **new_insn)
 733 {
 734         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 735         unsigned long dest_off;
 736
 737         last_orig_insn = NULL;
 738         insn = orig_insn;
 739         sec_for_each_insn_from(file, insn) {
 740                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 741                         break;
 742
 743                 insn->alt_group = true;
 744                 last_orig_insn = insn;
 745         }
 746
 747         if (next_insn_same_sec(file, last_orig_insn)) {
 748                 fake_jump = malloc(sizeof(*fake_jump));
 749                 if (!fake_jump) {
 750                         WARN("malloc failed");
 751                         return -1;
 752                 }
 753                 memset(fake_jump, 0, sizeof(*fake_jump));
 754                 INIT_LIST_HEAD(&fake_jump->alts);
 755                 clear_insn_state(&fake_jump->state);
 756
 757                 fake_jump->sec = special_alt->new_sec;
 758                 fake_jump->offset = FAKE_JUMP_OFFSET;
 759                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 760                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 761                 fake_jump->func = orig_insn->func;
 762         }
 763
 764         if (!special_alt->new_len) {
 765                 if (!fake_jump) {
 766                         WARN("%s: empty alternative at end of section",
 767                              special_alt->orig_sec->name);
 768                         return -1;
 769                 }
 770
 771                 *new_insn = fake_jump;
 772                 return 0;
 773         }
 774
 775         last_new_insn = NULL;
 776         insn = *new_insn;
 777         sec_for_each_insn_from(file, insn) {
 778                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 779                         break;
 780
 781                 last_new_insn = insn;
 782
 783                 insn->ignore = orig_insn->ignore_alts;
 784                 insn->func = orig_insn->func;
 785
 786                 /*
 787                  * Since alternative replacement code is copy/pasted by the
 788                  * kernel after applying relocations, generally such code can't
 789                  * have relative-address relocation references to outside the
 790                  * .altinstr_replacement section, unless the arch's
 791                  * alternatives code can adjust the relative offsets
 792                  * accordingly.
 793                  *
 794                  * The x86 alternatives code adjusts the offsets only when it
 795                  * encounters a branch instruction at the very beginning of the
 796                  * replacement group.
 797                  */
 798                 if ((insn->offset != special_alt->new_off ||
 799                     (insn->type != INSN_CALL && !is_static_jump(insn))) &&
 800                     find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
 801
 802                         WARN_FUNC("unsupported relocation in alternatives section",
 803                                   insn->sec, insn->offset);
 804                         return -1;
 805                 }
 806
 807                 if (!is_static_jump(insn))
 808                         continue;
 809
 810                 if (!insn->immediate)
 811                         continue;
 812
 813                 dest_off = insn->offset + insn->len + insn->immediate;
 814                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 815                         if (!fake_jump) {
 816                                 WARN("%s: alternative jump to end of section",
 817                                      special_alt->orig_sec->name);
 818                                 return -1;
 819                         }
 820                         insn->jump_dest = fake_jump;
 821                 }
 822
 823                 if (!insn->jump_dest) {
 824                         WARN_FUNC("can't find alternative jump destination",
 825                                   insn->sec, insn->offset);
 826                         return -1;
 827                 }
 828         }
 829
 830         if (!last_new_insn) {
 831                 WARN_FUNC("can't find last new alternative instruction",
 832                           special_alt->new_sec, special_alt->new_off);
 833                 return -1;
 834         }
 835
 836         if (fake_jump)
 837                 list_add(&fake_jump->list, &last_new_insn->list);
 838
 839         return 0;
 840 }
 841
 842 /*
 843  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 844  * If the original instruction is a jump, make the alt entry an effective nop
 845  * by just skipping the original instruction.
 846  */
 847 static int handle_jump_alt(struct objtool_file *file,
 848                            struct special_alt *special_alt,
 849                            struct instruction *orig_insn,
 850                            struct instruction **new_insn)
 851 {
 852         if (orig_insn->type == INSN_NOP)
 853                 return 0;
 854
 855         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 856                 WARN_FUNC("unsupported instruction at jump label",
 857                           orig_insn->sec, orig_insn->offset);
 858                 return -1;
 859         }
 860
 861         *new_insn = list_next_entry(orig_insn, list);
 862         return 0;
 863 }
 864
 865 /*
 866  * Read all the special sections which have alternate instructions which can be
 867  * patched in or redirected to at runtime.  Each instruction having alternate
 868  * instruction(s) has them added to its insn->alts list, which will be
 869  * traversed in validate_branch().
 870  */
 871 static int add_special_section_alts(struct objtool_file *file)
 872 {
 873         struct list_head special_alts;
 874         struct instruction *orig_insn, *new_insn;
 875         struct special_alt *special_alt, *tmp;
 876         struct alternative *alt;
 877         int ret;
 878
 879         ret = special_get_alts(file->elf, &special_alts);
 880         if (ret)
 881                 return ret;
 882
 883         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 884
 885                 orig_insn = find_insn(file, special_alt->orig_sec,
 886                                       special_alt->orig_off);
 887                 if (!orig_insn) {
 888                         WARN_FUNC("special: can't find orig instruction",
 889                                   special_alt->orig_sec, special_alt->orig_off);
 890                         ret = -1;
 891                         goto out;
 892                 }
 893
 894                 new_insn = NULL;
 895                 if (!special_alt->group || special_alt->new_len) {
 896                         new_insn = find_insn(file, special_alt->new_sec,
 897                                              special_alt->new_off);
 898                         if (!new_insn) {
 899                                 WARN_FUNC("special: can't find new instruction",
 900                                           special_alt->new_sec,
 901                                           special_alt->new_off);
 902                                 ret = -1;
 903                                 goto out;
 904                         }
 905                 }
 906
 907                 if (special_alt->group) {
 908                         ret = handle_group_alt(file, special_alt, orig_insn,
 909                                                &new_insn);
 910                         if (ret)
 911                                 goto out;
 912                 } else if (special_alt->jump_or_nop) {
 913                         ret = handle_jump_alt(file, special_alt, orig_insn,
 914                                               &new_insn);
 915                         if (ret)
 916                                 goto out;
 917                 }
 918
 919                 alt = malloc(sizeof(*alt));
 920                 if (!alt) {
 921                         WARN("malloc failed");
 922                         ret = -1;
 923                         goto out;
 924                 }
 925
 926                 alt->insn = new_insn;
 927                 alt->skip_orig = special_alt->skip_orig;
 928                 orig_insn->ignore_alts |= special_alt->skip_alt;
 929                 list_add_tail(&alt->list, &orig_insn->alts);
 930
 931                 list_del(&special_alt->list);
 932                 free(special_alt);
 933         }
 934
 935 out:
 936         return ret;
 937 }
 938
 939 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 940                             struct rela *table)
 941 {
 942         struct rela *rela = table;
 943         struct instruction *dest_insn;
 944         struct alternative *alt;
 945         struct symbol *pfunc = insn->func->pfunc;
 946         unsigned int prev_offset = 0;
 947
 948         /*
 949          * Each @rela is a switch table relocation which points to the target
 950          * instruction.
 951          */
 952         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 953
 954                 /* Check for the end of the table: */
 955                 if (rela != table && rela->jump_table_start)
 956                         break;
 957
 958                 /* Make sure the table entries are consecutive: */
 959                 if (prev_offset && rela->offset != prev_offset + 8)
 960                         break;
 961
 962                 /* Detect function pointers from contiguous objects: */
 963                 if (rela->sym->sec == pfunc->sec &&
 964                     rela->addend == pfunc->offset)
 965                         break;
 966
 967                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 968                 if (!dest_insn)
 969                         break;
 970
 971                 /* Make sure the destination is in the same function: */
 972                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 973                         break;
 974
 975                 alt = malloc(sizeof(*alt));
 976                 if (!alt) {
 977                         WARN("malloc failed");
 978                         return -1;
 979                 }
 980
 981                 alt->insn = dest_insn;
 982                 list_add_tail(&alt->list, &insn->alts);
 983                 prev_offset = rela->offset;
 984         }
 985
 986         if (!prev_offset) {
 987                 WARN_FUNC("can't find switch jump table",
 988                           insn->sec, insn->offset);
 989                 return -1;
 990         }
 991
 992         return 0;
 993 }
 994
 995 /*
 996  * find_jump_table() - Given a dynamic jump, find the switch jump table in
 997  * .rodata associated with it.
 998  *
 999  * There are 3 basic patterns:
1000  *
1001  * 1. jmpq *[rodata addr](,%reg,8)
1002  *
1003  *    This is the most common case by far.  It jumps to an address in a simple
1004  *    jump table which is stored in .rodata.
1005  *
1006  * 2. jmpq *[rodata addr](%rip)
1007  *
1008  *    This is caused by a rare GCC quirk, currently only seen in three driver
1009  *    functions in the kernel, only with certain obscure non-distro configs.
1010  *
1011  *    As part of an optimization, GCC makes a copy of an existing switch jump
1012  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
1013  *    jump) to use a single entry in the table.  The rest of the jump table and
1014  *    some of its jump targets remain as dead code.
1015  *
1016  *    In such a case we can just crudely ignore all unreachable instruction
1017  *    warnings for the entire object file.  Ideally we would just ignore them
1018  *    for the function, but that would require redesigning the code quite a
1019  *    bit.  And honestly that's just not worth doing: unreachable instruction
1020  *    warnings are of questionable value anyway, and this is such a rare issue.
1021  *
1022  * 3. mov [rodata addr],%reg1
1023  *    ... some instructions ...
1024  *    jmpq *(%reg1,%reg2,8)
1025  *
1026  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
1027  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
1028  *
1029  *    As of GCC 7 there are quite a few more of these and the 'in between' code
1030  *    is significant. Esp. with KASAN enabled some of the code between the mov
1031  *    and jmpq uses .rodata itself, which can confuse things.
1032  *
1033  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1034  *    ensure the same register is used in the mov and jump instructions.
1035  *
1036  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1037  */
1038 static struct rela *find_jump_table(struct objtool_file *file,
1039                                       struct symbol *func,
1040                                       struct instruction *insn)
1041 {
1042         struct rela *text_rela, *table_rela;
1043         struct instruction *dest_insn, *orig_insn = insn;
1044         struct section *table_sec;
1045         unsigned long table_offset;
1046
1047         /*
1048          * Backward search using the @first_jump_src links, these help avoid
1049          * much of the 'in between' code. Which avoids us getting confused by
1050          * it.
1051          */
1052         for (;
1053              &insn->list != &file->insn_list &&
1054              insn->sec == func->sec &&
1055              insn->offset >= func->offset;
1056
1057              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1058
1059                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1060                         break;
1061
1062                 /* allow small jumps within the range */
1063                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1064                     insn->jump_dest &&
1065                     (insn->jump_dest->offset <= insn->offset ||
1066                      insn->jump_dest->offset > orig_insn->offset))
1067                     break;
1068
1069                 /* look for a relocation which references .rodata */
1070                 text_rela = find_rela_by_dest_range(file->elf, insn->sec,
1071                                                     insn->offset, insn->len);
1072                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1073                     !text_rela->sym->sec->rodata)
1074                         continue;
1075
1076                 table_offset = text_rela->addend;
1077                 table_sec = text_rela->sym->sec;
1078
1079                 if (text_rela->type == R_X86_64_PC32)
1080                         table_offset += 4;
1081
1082                 /*
1083                  * Make sure the .rodata address isn't associated with a
1084                  * symbol.  GCC jump tables are anonymous data.
1085                  *
1086                  * Also support C jump tables which are in the same format as
1087                  * switch jump tables.  For objtool to recognize them, they
1088                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1089                  * have symbols associated with them.
1090                  */
1091                 if (find_symbol_containing(table_sec, table_offset) &&
1092                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1093                         continue;
1094
1095                 /*
1096                  * Each table entry has a rela associated with it.  The rela
1097                  * should reference text in the same function as the original
1098                  * instruction.
1099                  */
1100                 table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
1101                 if (!table_rela)
1102                         continue;
1103                 dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
1104                 if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
1105                         continue;
1106
1107                 /*
1108                  * Use of RIP-relative switch jumps is quite rare, and
1109                  * indicates a rare GCC quirk/bug which can leave dead code
1110                  * behind.
1111                  */
1112                 if (text_rela->type == R_X86_64_PC32)
1113                         file->ignore_unreachables = true;
1114
1115                 return table_rela;
1116         }
1117
1118         return NULL;
1119 }
1120
1121 /*
1122  * First pass: Mark the head of each jump table so that in the next pass,
1123  * we know when a given jump table ends and the next one starts.
1124  */
1125 static void mark_func_jump_tables(struct objtool_file *file,
1126                                     struct symbol *func)
1127 {
1128         struct instruction *insn, *last = NULL;
1129         struct rela *rela;
1130
1131         func_for_each_insn(file, func, insn) {
1132                 if (!last)
1133                         last = insn;
1134
1135                 /*
1136                  * Store back-pointers for unconditional forward jumps such
1137                  * that find_jump_table() can back-track using those and
1138                  * avoid some potentially confusing code.
1139                  */
1140                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1141                     insn->offset > last->offset &&
1142                     insn->jump_dest->offset > insn->offset &&
1143                     !insn->jump_dest->first_jump_src) {
1144
1145                         insn->jump_dest->first_jump_src = insn;
1146                         last = insn->jump_dest;
1147                 }
1148
1149                 if (insn->type != INSN_JUMP_DYNAMIC)
1150                         continue;
1151
1152                 rela = find_jump_table(file, func, insn);
1153                 if (rela) {
1154                         rela->jump_table_start = true;
1155                         insn->jump_table = rela;
1156                 }
1157         }
1158 }
1159
1160 static int add_func_jump_tables(struct objtool_file *file,
1161                                   struct symbol *func)
1162 {
1163         struct instruction *insn;
1164         int ret;
1165
1166         func_for_each_insn(file, func, insn) {
1167                 if (!insn->jump_table)
1168                         continue;
1169
1170                 ret = add_jump_table(file, insn, insn->jump_table);
1171                 if (ret)
1172                         return ret;
1173         }
1174
1175         return 0;
1176 }
1177
1178 /*
1179  * For some switch statements, gcc generates a jump table in the .rodata
1180  * section which contains a list of addresses within the function to jump to.
1181  * This finds these jump tables and adds them to the insn->alts lists.
1182  */
1183 static int add_jump_table_alts(struct objtool_file *file)
1184 {
1185         struct section *sec;
1186         struct symbol *func;
1187         int ret;
1188
1189         if (!file->rodata)
1190                 return 0;
1191
1192         for_each_sec(file, sec) {
1193                 list_for_each_entry(func, &sec->symbol_list, list) {
1194                         if (func->type != STT_FUNC)
1195                                 continue;
1196
1197                         mark_func_jump_tables(file, func);
1198                         ret = add_func_jump_tables(file, func);
1199                         if (ret)
1200                                 return ret;
1201                 }
1202         }
1203
1204         return 0;
1205 }
1206
1207 static int read_unwind_hints(struct objtool_file *file)
1208 {
1209         struct section *sec, *relasec;
1210         struct rela *rela;
1211         struct unwind_hint *hint;
1212         struct instruction *insn;
1213         struct cfi_reg *cfa;
1214         int i;
1215
1216         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1217         if (!sec)
1218                 return 0;
1219
1220         relasec = sec->rela;
1221         if (!relasec) {
1222                 WARN("missing .rela.discard.unwind_hints section");
1223                 return -1;
1224         }
1225
1226         if (sec->len % sizeof(struct unwind_hint)) {
1227                 WARN("struct unwind_hint size mismatch");
1228                 return -1;
1229         }
1230
1231         file->hints = true;
1232
1233         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1234                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1235
1236                 rela = find_rela_by_dest(file->elf, sec, i * sizeof(*hint));
1237                 if (!rela) {
1238                         WARN("can't find rela for unwind_hints[%d]", i);
1239                         return -1;
1240                 }
1241
1242                 insn = find_insn(file, rela->sym->sec, rela->addend);
1243                 if (!insn) {
1244                         WARN("can't find insn for unwind_hints[%d]", i);
1245                         return -1;
1246                 }
1247
1248                 cfa = &insn->state.cfa;
1249
1250                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1251                         insn->save = true;
1252                         continue;
1253
1254                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1255                         insn->restore = true;
1256                         insn->hint = true;
1257                         continue;
1258                 }
1259
1260                 insn->hint = true;
1261
1262                 switch (hint->sp_reg) {
1263                 case ORC_REG_UNDEFINED:
1264                         cfa->base = CFI_UNDEFINED;
1265                         break;
1266                 case ORC_REG_SP:
1267                         cfa->base = CFI_SP;
1268                         break;
1269                 case ORC_REG_BP:
1270                         cfa->base = CFI_BP;
1271                         break;
1272                 case ORC_REG_SP_INDIRECT:
1273                         cfa->base = CFI_SP_INDIRECT;
1274                         break;
1275                 case ORC_REG_R10:
1276                         cfa->base = CFI_R10;
1277                         break;
1278                 case ORC_REG_R13:
1279                         cfa->base = CFI_R13;
1280                         break;
1281                 case ORC_REG_DI:
1282                         cfa->base = CFI_DI;
1283                         break;
1284                 case ORC_REG_DX:
1285                         cfa->base = CFI_DX;
1286                         break;
1287                 default:
1288                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1289                                   insn->sec, insn->offset, hint->sp_reg);
1290                         return -1;
1291                 }
1292
1293                 cfa->offset = hint->sp_offset;
1294                 insn->state.type = hint->type;
1295                 insn->state.end = hint->end;
1296         }
1297
1298         return 0;
1299 }
1300
1301 static int read_retpoline_hints(struct objtool_file *file)
1302 {
1303         struct section *sec;
1304         struct instruction *insn;
1305         struct rela *rela;
1306
1307         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1308         if (!sec)
1309                 return 0;
1310
1311         list_for_each_entry(rela, &sec->rela_list, list) {
1312                 if (rela->sym->type != STT_SECTION) {
1313                         WARN("unexpected relocation symbol type in %s", sec->name);
1314                         return -1;
1315                 }
1316
1317                 insn = find_insn(file, rela->sym->sec, rela->addend);
1318                 if (!insn) {
1319                         WARN("bad .discard.retpoline_safe entry");
1320                         return -1;
1321                 }
1322
1323                 if (insn->type != INSN_JUMP_DYNAMIC &&
1324                     insn->type != INSN_CALL_DYNAMIC) {
1325                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1326                                   insn->sec, insn->offset);
1327                         return -1;
1328                 }
1329
1330                 insn->retpoline_safe = true;
1331         }
1332
1333         return 0;
1334 }
1335
1336 static void mark_rodata(struct objtool_file *file)
1337 {
1338         struct section *sec;
1339         bool found = false;
1340
1341         /*
1342          * Search for the following rodata sections, each of which can
1343          * potentially contain jump tables:
1344          *
1345          * - .rodata: can contain GCC switch tables
1346          * - .rodata.<func>: same, if -fdata-sections is being used
1347          * - .rodata..c_jump_table: contains C annotated jump tables
1348          *
1349          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1350          */
1351         for_each_sec(file, sec) {
1352                 if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
1353                     !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
1354                         sec->rodata = true;
1355                         found = true;
1356                 }
1357         }
1358
1359         file->rodata = found;
1360 }
1361
1362 static int decode_sections(struct objtool_file *file)
1363 {
1364         int ret;
1365
1366         mark_rodata(file);
1367
1368         ret = decode_instructions(file);
1369         if (ret)
1370                 return ret;
1371
1372         ret = add_dead_ends(file);
1373         if (ret)
1374                 return ret;
1375
1376         add_ignores(file);
1377         add_uaccess_safe(file);
1378
1379         ret = add_ignore_alternatives(file);
1380         if (ret)
1381                 return ret;
1382
1383         ret = add_jump_destinations(file);
1384         if (ret)
1385                 return ret;
1386
1387         ret = add_special_section_alts(file);
1388         if (ret)
1389                 return ret;
1390
1391         ret = add_call_destinations(file);
1392         if (ret)
1393                 return ret;
1394
1395         ret = add_jump_table_alts(file);
1396         if (ret)
1397                 return ret;
1398
1399         ret = read_unwind_hints(file);
1400         if (ret)
1401                 return ret;
1402
1403         ret = read_retpoline_hints(file);
1404         if (ret)
1405                 return ret;
1406
1407         return 0;
1408 }
1409
1410 static bool is_fentry_call(struct instruction *insn)
1411 {
1412         if (insn->type == INSN_CALL &&
1413             insn->call_dest->type == STT_NOTYPE &&
1414             !strcmp(insn->call_dest->name, "__fentry__"))
1415                 return true;
1416
1417         return false;
1418 }
1419
1420 static bool has_modified_stack_frame(struct insn_state *state)
1421 {
1422         int i;
1423
1424         if (state->cfa.base != initial_func_cfi.cfa.base ||
1425             state->cfa.offset != initial_func_cfi.cfa.offset ||
1426             state->stack_size != initial_func_cfi.cfa.offset ||
1427             state->drap)
1428                 return true;
1429
1430         for (i = 0; i < CFI_NUM_REGS; i++)
1431                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1432                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1433                         return true;
1434
1435         return false;
1436 }
1437
1438 static bool has_valid_stack_frame(struct insn_state *state)
1439 {
1440         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1441             state->regs[CFI_BP].offset == -16)
1442                 return true;
1443
1444         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1445                 return true;
1446
1447         return false;
1448 }
1449
1450 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1451 {
1452         struct cfi_reg *cfa = &state->cfa;
1453         struct stack_op *op = &insn->stack_op;
1454
1455         if (cfa->base != CFI_SP)
1456                 return 0;
1457
1458         /* push */
1459         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1460                 cfa->offset += 8;
1461
1462         /* pop */
1463         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1464                 cfa->offset -= 8;
1465
1466         /* add immediate to sp */
1467         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1468             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1469                 cfa->offset -= op->src.offset;
1470
1471         return 0;
1472 }
1473
1474 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1475                      int offset)
1476 {
1477         if (arch_callee_saved_reg(reg) &&
1478             state->regs[reg].base == CFI_UNDEFINED) {
1479                 state->regs[reg].base = base;
1480                 state->regs[reg].offset = offset;
1481         }
1482 }
1483
1484 static void restore_reg(struct insn_state *state, unsigned char reg)
1485 {
1486         state->regs[reg].base = CFI_UNDEFINED;
1487         state->regs[reg].offset = 0;
1488 }
1489
1490 /*
1491  * A note about DRAP stack alignment:
1492  *
1493  * GCC has the concept of a DRAP register, which is used to help keep track of
1494  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1495  * register.  The typical DRAP pattern is:
1496  *
1497  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1498  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1499  *   41 ff 72 f8                pushq  -0x8(%r10)
1500  *   55                         push   %rbp
1501  *   48 89 e5                   mov    %rsp,%rbp
1502  *                              (more pushes)
1503  *   41 52                      push   %r10
1504  *                              ...
1505  *   41 5a                      pop    %r10
1506  *                              (more pops)
1507  *   5d                         pop    %rbp
1508  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1509  *   c3                         retq
1510  *
1511  * There are some variations in the epilogues, like:
1512  *
1513  *   5b                         pop    %rbx
1514  *   41 5a                      pop    %r10
1515  *   41 5c                      pop    %r12
1516  *   41 5d                      pop    %r13
1517  *   41 5e                      pop    %r14
1518  *   c9                         leaveq
1519  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1520  *   c3                         retq
1521  *
1522  * and:
1523  *
1524  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1525  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1526  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1527  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1528  *   c9                         leaveq
1529  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1530  *   c3                         retq
1531  *
1532  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1533  * restored beforehand:
1534  *
1535  *   41 55                      push   %r13
1536  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1537  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1538  *                              ...
1539  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1540  *   41 5d                      pop    %r13
1541  *   c3                         retq
1542  */
1543 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1544 {
1545         struct stack_op *op = &insn->stack_op;
1546         struct cfi_reg *cfa = &state->cfa;
1547         struct cfi_reg *regs = state->regs;
1548
1549         /* stack operations don't make sense with an undefined CFA */
1550         if (cfa->base == CFI_UNDEFINED) {
1551                 if (insn->func) {
1552                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1553                         return -1;
1554                 }
1555                 return 0;
1556         }
1557
1558         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1559                 return update_insn_state_regs(insn, state);
1560
1561         switch (op->dest.type) {
1562
1563         case OP_DEST_REG:
1564                 switch (op->src.type) {
1565
1566                 case OP_SRC_REG:
1567                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1568                             cfa->base == CFI_SP &&
1569                             regs[CFI_BP].base == CFI_CFA &&
1570                             regs[CFI_BP].offset == -cfa->offset) {
1571
1572                                 /* mov %rsp, %rbp */
1573                                 cfa->base = op->dest.reg;
1574                                 state->bp_scratch = false;
1575                         }
1576
1577                         else if (op->src.reg == CFI_SP &&
1578                                  op->dest.reg == CFI_BP && state->drap) {
1579
1580                                 /* drap: mov %rsp, %rbp */
1581                                 regs[CFI_BP].base = CFI_BP;
1582                                 regs[CFI_BP].offset = -state->stack_size;
1583                                 state->bp_scratch = false;
1584                         }
1585
1586                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1587
1588                                 /*
1589                                  * mov %rsp, %reg
1590                                  *
1591                                  * This is needed for the rare case where GCC
1592                                  * does:
1593                                  *
1594                                  *   mov    %rsp, %rax
1595                                  *   ...
1596                                  *   mov    %rax, %rsp
1597                                  */
1598                                 state->vals[op->dest.reg].base = CFI_CFA;
1599                                 state->vals[op->dest.reg].offset = -state->stack_size;
1600                         }
1601
1602                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1603                                  cfa->base == CFI_BP) {
1604
1605                                 /*
1606                                  * mov %rbp, %rsp
1607                                  *
1608                                  * Restore the original stack pointer (Clang).
1609                                  */
1610                                 state->stack_size = -state->regs[CFI_BP].offset;
1611                         }
1612
1613                         else if (op->dest.reg == cfa->base) {
1614
1615                                 /* mov %reg, %rsp */
1616                                 if (cfa->base == CFI_SP &&
1617                                     state->vals[op->src.reg].base == CFI_CFA) {
1618
1619                                         /*
1620                                          * This is needed for the rare case
1621                                          * where GCC does something dumb like:
1622                                          *
1623                                          *   lea    0x8(%rsp), %rcx
1624                                          *   ...
1625                                          *   mov    %rcx, %rsp
1626                                          */
1627                                         cfa->offset = -state->vals[op->src.reg].offset;
1628                                         state->stack_size = cfa->offset;
1629
1630                                 } else {
1631                                         cfa->base = CFI_UNDEFINED;
1632                                         cfa->offset = 0;
1633                                 }
1634                         }
1635
1636                         break;
1637
1638                 case OP_SRC_ADD:
1639                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1640
1641                                 /* add imm, %rsp */
1642                                 state->stack_size -= op->src.offset;
1643                                 if (cfa->base == CFI_SP)
1644                                         cfa->offset -= op->src.offset;
1645                                 break;
1646                         }
1647
1648                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1649
1650                                 /* lea disp(%rbp), %rsp */
1651                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1652                                 break;
1653                         }
1654
1655                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1656
1657                                 /* drap: lea disp(%rsp), %drap */
1658                                 state->drap_reg = op->dest.reg;
1659
1660                                 /*
1661                                  * lea disp(%rsp), %reg
1662                                  *
1663                                  * This is needed for the rare case where GCC
1664                                  * does something dumb like:
1665                                  *
1666                                  *   lea    0x8(%rsp), %rcx
1667                                  *   ...
1668                                  *   mov    %rcx, %rsp
1669                                  */
1670                                 state->vals[op->dest.reg].base = CFI_CFA;
1671                                 state->vals[op->dest.reg].offset = \
1672                                         -state->stack_size + op->src.offset;
1673
1674                                 break;
1675                         }
1676
1677                         if (state->drap && op->dest.reg == CFI_SP &&
1678                             op->src.reg == state->drap_reg) {
1679
1680                                  /* drap: lea disp(%drap), %rsp */
1681                                 cfa->base = CFI_SP;
1682                                 cfa->offset = state->stack_size = -op->src.offset;
1683                                 state->drap_reg = CFI_UNDEFINED;
1684                                 state->drap = false;
1685                                 break;
1686                         }
1687
1688                         if (op->dest.reg == state->cfa.base) {
1689                                 WARN_FUNC("unsupported stack register modification",
1690                                           insn->sec, insn->offset);
1691                                 return -1;
1692                         }
1693
1694                         break;
1695
1696                 case OP_SRC_AND:
1697                         if (op->dest.reg != CFI_SP ||
1698                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1699                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1700                                 WARN_FUNC("unsupported stack pointer realignment",
1701                                           insn->sec, insn->offset);
1702                                 return -1;
1703                         }
1704
1705                         if (state->drap_reg != CFI_UNDEFINED) {
1706                                 /* drap: and imm, %rsp */
1707                                 cfa->base = state->drap_reg;
1708                                 cfa->offset = state->stack_size = 0;
1709                                 state->drap = true;
1710                         }
1711
1712                         /*
1713                          * Older versions of GCC (4.8ish) realign the stack
1714                          * without DRAP, with a frame pointer.
1715                          */
1716
1717                         break;
1718
1719                 case OP_SRC_POP:
1720                 case OP_SRC_POPF:
1721                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1722                             op->dest.reg == cfa->base) {
1723
1724                                 /* pop %rbp */
1725                                 cfa->base = CFI_SP;
1726                         }
1727
1728                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1729                             op->dest.type == OP_DEST_REG &&
1730                             op->dest.reg == state->drap_reg &&
1731                             state->drap_offset == -state->stack_size) {
1732
1733                                 /* drap: pop %drap */
1734                                 cfa->base = state->drap_reg;
1735                                 cfa->offset = 0;
1736                                 state->drap_offset = -1;
1737
1738                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1739
1740                                 /* pop %reg */
1741                                 restore_reg(state, op->dest.reg);
1742                         }
1743
1744                         state->stack_size -= 8;
1745                         if (cfa->base == CFI_SP)
1746                                 cfa->offset -= 8;
1747
1748                         break;
1749
1750                 case OP_SRC_REG_INDIRECT:
1751                         if (state->drap && op->src.reg == CFI_BP &&
1752                             op->src.offset == state->drap_offset) {
1753
1754                                 /* drap: mov disp(%rbp), %drap */
1755                                 cfa->base = state->drap_reg;
1756                                 cfa->offset = 0;
1757                                 state->drap_offset = -1;
1758                         }
1759
1760                         if (state->drap && op->src.reg == CFI_BP &&
1761                             op->src.offset == regs[op->dest.reg].offset) {
1762
1763                                 /* drap: mov disp(%rbp), %reg */
1764                                 restore_reg(state, op->dest.reg);
1765
1766                         } else if (op->src.reg == cfa->base &&
1767                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1768
1769                                 /* mov disp(%rbp), %reg */
1770                                 /* mov disp(%rsp), %reg */
1771                                 restore_reg(state, op->dest.reg);
1772                         }
1773
1774                         break;
1775
1776                 default:
1777                         WARN_FUNC("unknown stack-related instruction",
1778                                   insn->sec, insn->offset);
1779                         return -1;
1780                 }
1781
1782                 break;
1783
1784         case OP_DEST_PUSH:
1785         case OP_DEST_PUSHF:
1786                 state->stack_size += 8;
1787                 if (cfa->base == CFI_SP)
1788                         cfa->offset += 8;
1789
1790                 if (op->src.type != OP_SRC_REG)
1791                         break;
1792
1793                 if (state->drap) {
1794                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1795
1796                                 /* drap: push %drap */
1797                                 cfa->base = CFI_BP_INDIRECT;
1798                                 cfa->offset = -state->stack_size;
1799
1800                                 /* save drap so we know when to restore it */
1801                                 state->drap_offset = -state->stack_size;
1802
1803                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1804
1805                                 /* drap: push %rbp */
1806                                 state->stack_size = 0;
1807
1808                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1809
1810                                 /* drap: push %reg */
1811                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1812                         }
1813
1814                 } else {
1815
1816                         /* push %reg */
1817                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1818                 }
1819
1820                 /* detect when asm code uses rbp as a scratch register */
1821                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1822                     cfa->base != CFI_BP)
1823                         state->bp_scratch = true;
1824                 break;
1825
1826         case OP_DEST_REG_INDIRECT:
1827
1828                 if (state->drap) {
1829                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1830
1831                                 /* drap: mov %drap, disp(%rbp) */
1832                                 cfa->base = CFI_BP_INDIRECT;
1833                                 cfa->offset = op->dest.offset;
1834
1835                                 /* save drap offset so we know when to restore it */
1836                                 state->drap_offset = op->dest.offset;
1837                         }
1838
1839                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1840
1841                                 /* drap: mov reg, disp(%rbp) */
1842                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1843                         }
1844
1845                 } else if (op->dest.reg == cfa->base) {
1846
1847                         /* mov reg, disp(%rbp) */
1848                         /* mov reg, disp(%rsp) */
1849                         save_reg(state, op->src.reg, CFI_CFA,
1850                                  op->dest.offset - state->cfa.offset);
1851                 }
1852
1853                 break;
1854
1855         case OP_DEST_LEAVE:
1856                 if ((!state->drap && cfa->base != CFI_BP) ||
1857                     (state->drap && cfa->base != state->drap_reg)) {
1858                         WARN_FUNC("leave instruction with modified stack frame",
1859                                   insn->sec, insn->offset);
1860                         return -1;
1861                 }
1862
1863                 /* leave (mov %rbp, %rsp; pop %rbp) */
1864
1865                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1866                 restore_reg(state, CFI_BP);
1867
1868                 if (!state->drap) {
1869                         cfa->base = CFI_SP;
1870                         cfa->offset -= 8;
1871                 }
1872
1873                 break;
1874
1875         case OP_DEST_MEM:
1876                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1877                         WARN_FUNC("unknown stack-related memory operation",
1878                                   insn->sec, insn->offset);
1879                         return -1;
1880                 }
1881
1882                 /* pop mem */
1883                 state->stack_size -= 8;
1884                 if (cfa->base == CFI_SP)
1885                         cfa->offset -= 8;
1886
1887                 break;
1888
1889         default:
1890                 WARN_FUNC("unknown stack-related instruction",
1891                           insn->sec, insn->offset);
1892                 return -1;
1893         }
1894
1895         return 0;
1896 }
1897
1898 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1899 {
1900         struct insn_state *state1 = &insn->state, *state2 = state;
1901         int i;
1902
1903         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1904                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1905                           insn->sec, insn->offset,
1906                           state1->cfa.base, state1->cfa.offset,
1907                           state2->cfa.base, state2->cfa.offset);
1908
1909         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1910                 for (i = 0; i < CFI_NUM_REGS; i++) {
1911                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1912                                     sizeof(struct cfi_reg)))
1913                                 continue;
1914
1915                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1916                                   insn->sec, insn->offset,
1917                                   i, state1->regs[i].base, state1->regs[i].offset,
1918                                   i, state2->regs[i].base, state2->regs[i].offset);
1919                         break;
1920                 }
1921
1922         } else if (state1->type != state2->type) {
1923                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1924                           insn->sec, insn->offset, state1->type, state2->type);
1925
1926         } else if (state1->drap != state2->drap ||
1927                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1928                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1929                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1930                           insn->sec, insn->offset,
1931                           state1->drap, state1->drap_reg, state1->drap_offset,
1932                           state2->drap, state2->drap_reg, state2->drap_offset);
1933
1934         } else
1935                 return true;
1936
1937         return false;
1938 }
1939
1940 static inline bool func_uaccess_safe(struct symbol *func)
1941 {
1942         if (func)
1943                 return func->uaccess_safe;
1944
1945         return false;
1946 }
1947
1948 static inline const char *call_dest_name(struct instruction *insn)
1949 {
1950         if (insn->call_dest)
1951                 return insn->call_dest->name;
1952
1953         return "{dynamic}";
1954 }
1955
1956 static int validate_call(struct instruction *insn, struct insn_state *state)
1957 {
1958         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1959                 WARN_FUNC("call to %s() with UACCESS enabled",
1960                                 insn->sec, insn->offset, call_dest_name(insn));
1961                 return 1;
1962         }
1963
1964         if (state->df) {
1965                 WARN_FUNC("call to %s() with DF set",
1966                                 insn->sec, insn->offset, call_dest_name(insn));
1967                 return 1;
1968         }
1969
1970         return 0;
1971 }
1972
1973 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1974 {
1975         if (has_modified_stack_frame(state)) {
1976                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1977                                 insn->sec, insn->offset);
1978                 return 1;
1979         }
1980
1981         return validate_call(insn, state);
1982 }
1983
1984 static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
1985 {
1986         if (state->uaccess && !func_uaccess_safe(func)) {
1987                 WARN_FUNC("return with UACCESS enabled",
1988                           insn->sec, insn->offset);
1989                 return 1;
1990         }
1991
1992         if (!state->uaccess && func_uaccess_safe(func)) {
1993                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
1994                           insn->sec, insn->offset);
1995                 return 1;
1996         }
1997
1998         if (state->df) {
1999                 WARN_FUNC("return with DF set",
2000                           insn->sec, insn->offset);
2001                 return 1;
2002         }
2003
2004         if (func && has_modified_stack_frame(state)) {
2005                 WARN_FUNC("return with modified stack frame",
2006                           insn->sec, insn->offset);
2007                 return 1;
2008         }
2009
2010         if (state->bp_scratch) {
2011                 WARN("%s uses BP as a scratch register",
2012                      func->name);
2013                 return 1;
2014         }
2015
2016         return 0;
2017 }
2018
2019 /*
2020  * Follow the branch starting at the given instruction, and recursively follow
2021  * any other branches (jumps).  Meanwhile, track the frame pointer state at
2022  * each instruction and validate all the rules described in
2023  * tools/objtool/Documentation/stack-validation.txt.
2024  */
2025 static int validate_branch(struct objtool_file *file, struct symbol *func,
2026                            struct instruction *first, struct insn_state state)
2027 {
2028         struct alternative *alt;
2029         struct instruction *insn, *next_insn;
2030         struct section *sec;
2031         u8 visited;
2032         int ret;
2033
2034         insn = first;
2035         sec = insn->sec;
2036
2037         if (insn->alt_group && list_empty(&insn->alts)) {
2038                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
2039                           sec, insn->offset);
2040                 return 1;
2041         }
2042
2043         while (1) {
2044                 next_insn = next_insn_same_sec(file, insn);
2045
2046                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
2047                         WARN("%s() falls through to next function %s()",
2048                              func->name, insn->func->name);
2049                         return 1;
2050                 }
2051
2052                 if (func && insn->ignore) {
2053                         WARN_FUNC("BUG: why am I validating an ignored function?",
2054                                   sec, insn->offset);
2055                         return 1;
2056                 }
2057
2058                 visited = 1 << state.uaccess;
2059                 if (insn->visited) {
2060                         if (!insn->hint && !insn_state_match(insn, &state))
2061                                 return 1;
2062
2063                         if (insn->visited & visited)
2064                                 return 0;
2065                 }
2066
2067                 if (insn->hint) {
2068                         if (insn->restore) {
2069                                 struct instruction *save_insn, *i;
2070
2071                                 i = insn;
2072                                 save_insn = NULL;
2073                                 sym_for_each_insn_continue_reverse(file, func, i) {
2074                                         if (i->save) {
2075                                                 save_insn = i;
2076                                                 break;
2077                                         }
2078                                 }
2079
2080                                 if (!save_insn) {
2081                                         WARN_FUNC("no corresponding CFI save for CFI restore",
2082                                                   sec, insn->offset);
2083                                         return 1;
2084                                 }
2085
2086                                 if (!save_insn->visited) {
2087                                         /*
2088                                          * Oops, no state to copy yet.
2089                                          * Hopefully we can reach this
2090                                          * instruction from another branch
2091                                          * after the save insn has been
2092                                          * visited.
2093                                          */
2094                                         if (insn == first)
2095                                                 return 0;
2096
2097                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2098                                                   sec, insn->offset);
2099                                         return 1;
2100                                 }
2101
2102                                 insn->state = save_insn->state;
2103                         }
2104
2105                         state = insn->state;
2106
2107                 } else
2108                         insn->state = state;
2109
2110                 insn->visited |= visited;
2111
2112                 if (!insn->ignore_alts) {
2113                         bool skip_orig = false;
2114
2115                         list_for_each_entry(alt, &insn->alts, list) {
2116                                 if (alt->skip_orig)
2117                                         skip_orig = true;
2118
2119                                 ret = validate_branch(file, func, alt->insn, state);
2120                                 if (ret) {
2121                                         if (backtrace)
2122                                                 BT_FUNC("(alt)", insn);
2123                                         return ret;
2124                                 }
2125                         }
2126
2127                         if (skip_orig)
2128                                 return 0;
2129                 }
2130
2131                 switch (insn->type) {
2132
2133                 case INSN_RETURN:
2134                         return validate_return(func, insn, &state);
2135
2136                 case INSN_CALL:
2137                 case INSN_CALL_DYNAMIC:
2138                         ret = validate_call(insn, &state);
2139                         if (ret)
2140                                 return ret;
2141
2142                         if (!no_fp && func && !is_fentry_call(insn) &&
2143                             !has_valid_stack_frame(&state)) {
2144                                 WARN_FUNC("call without frame pointer save/setup",
2145                                           sec, insn->offset);
2146                                 return 1;
2147                         }
2148
2149                         if (dead_end_function(file, insn->call_dest))
2150                                 return 0;
2151
2152                         break;
2153
2154                 case INSN_JUMP_CONDITIONAL:
2155                 case INSN_JUMP_UNCONDITIONAL:
2156                         if (func && is_sibling_call(insn)) {
2157                                 ret = validate_sibling_call(insn, &state);
2158                                 if (ret)
2159                                         return ret;
2160
2161                         } else if (insn->jump_dest) {
2162                                 ret = validate_branch(file, func,
2163                                                       insn->jump_dest, state);
2164                                 if (ret) {
2165                                         if (backtrace)
2166                                                 BT_FUNC("(branch)", insn);
2167                                         return ret;
2168                                 }
2169                         }
2170
2171                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2172                                 return 0;
2173
2174                         break;
2175
2176                 case INSN_JUMP_DYNAMIC:
2177                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2178                         if (func && is_sibling_call(insn)) {
2179                                 ret = validate_sibling_call(insn, &state);
2180                                 if (ret)
2181                                         return ret;
2182                         }
2183
2184                         if (insn->type == INSN_JUMP_DYNAMIC)
2185                                 return 0;
2186
2187                         break;
2188
2189                 case INSN_CONTEXT_SWITCH:
2190                         if (func && (!next_insn || !next_insn->hint)) {
2191                                 WARN_FUNC("unsupported instruction in callable function",
2192                                           sec, insn->offset);
2193                                 return 1;
2194                         }
2195                         return 0;
2196
2197                 case INSN_STACK:
2198                         if (update_insn_state(insn, &state))
2199                                 return 1;
2200
2201                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2202                                 if (!state.uaccess_stack) {
2203                                         state.uaccess_stack = 1;
2204                                 } else if (state.uaccess_stack >> 31) {
2205                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2206                                         return 1;
2207                                 }
2208                                 state.uaccess_stack <<= 1;
2209                                 state.uaccess_stack  |= state.uaccess;
2210                         }
2211
2212                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2213                                 if (state.uaccess_stack) {
2214                                         state.uaccess = state.uaccess_stack & 1;
2215                                         state.uaccess_stack >>= 1;
2216                                         if (state.uaccess_stack == 1)
2217                                                 state.uaccess_stack = 0;
2218                                 }
2219                         }
2220
2221                         break;
2222
2223                 case INSN_STAC:
2224                         if (state.uaccess) {
2225                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2226                                 return 1;
2227                         }
2228
2229                         state.uaccess = true;
2230                         break;
2231
2232                 case INSN_CLAC:
2233                         if (!state.uaccess && func) {
2234                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2235                                 return 1;
2236                         }
2237
2238                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2239                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2240                                 return 1;
2241                         }
2242
2243                         state.uaccess = false;
2244                         break;
2245
2246                 case INSN_STD:
2247                         if (state.df)
2248                                 WARN_FUNC("recursive STD", sec, insn->offset);
2249
2250                         state.df = true;
2251                         break;
2252
2253                 case INSN_CLD:
2254                         if (!state.df && func)
2255                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2256
2257                         state.df = false;
2258                         break;
2259
2260                 default:
2261                         break;
2262                 }
2263
2264                 if (insn->dead_end)
2265                         return 0;
2266
2267                 if (!next_insn) {
2268                         if (state.cfa.base == CFI_UNDEFINED)
2269                                 return 0;
2270                         WARN("%s: unexpected end of section", sec->name);
2271                         return 1;
2272                 }
2273
2274                 insn = next_insn;
2275         }
2276
2277         return 0;
2278 }
2279
2280 static int validate_unwind_hints(struct objtool_file *file)
2281 {
2282         struct instruction *insn;
2283         int ret, warnings = 0;
2284         struct insn_state state;
2285
2286         if (!file->hints)
2287                 return 0;
2288
2289         clear_insn_state(&state);
2290
2291         for_each_insn(file, insn) {
2292                 if (insn->hint && !insn->visited) {
2293                         ret = validate_branch(file, insn->func, insn, state);
2294                         if (ret && backtrace)
2295                                 BT_FUNC("<=== (hint)", insn);
2296                         warnings += ret;
2297                 }
2298         }
2299
2300         return warnings;
2301 }
2302
2303 static int validate_retpoline(struct objtool_file *file)
2304 {
2305         struct instruction *insn;
2306         int warnings = 0;
2307
2308         for_each_insn(file, insn) {
2309                 if (insn->type != INSN_JUMP_DYNAMIC &&
2310                     insn->type != INSN_CALL_DYNAMIC)
2311                         continue;
2312
2313                 if (insn->retpoline_safe)
2314                         continue;
2315
2316                 /*
2317                  * .init.text code is ran before userspace and thus doesn't
2318                  * strictly need retpolines, except for modules which are
2319                  * loaded late, they very much do need retpoline in their
2320                  * .init.text
2321                  */
2322                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2323                         continue;
2324
2325                 WARN_FUNC("indirect %s found in RETPOLINE build",
2326                           insn->sec, insn->offset,
2327                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2328
2329                 warnings++;
2330         }
2331
2332         return warnings;
2333 }
2334
2335 static bool is_kasan_insn(struct instruction *insn)
2336 {
2337         return (insn->type == INSN_CALL &&
2338                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2339 }
2340
2341 static bool is_ubsan_insn(struct instruction *insn)
2342 {
2343         return (insn->type == INSN_CALL &&
2344                 !strcmp(insn->call_dest->name,
2345                         "__ubsan_handle_builtin_unreachable"));
2346 }
2347
2348 static bool ignore_unreachable_insn(struct instruction *insn)
2349 {
2350         int i;
2351
2352         if (insn->ignore || insn->type == INSN_NOP)
2353                 return true;
2354
2355         /*
2356          * Ignore any unused exceptions.  This can happen when a whitelisted
2357          * function has an exception table entry.
2358          *
2359          * Also ignore alternative replacement instructions.  This can happen
2360          * when a whitelisted function uses one of the ALTERNATIVE macros.
2361          */
2362         if (!strcmp(insn->sec->name, ".fixup") ||
2363             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2364             !strcmp(insn->sec->name, ".altinstr_aux"))
2365                 return true;
2366
2367         /*
2368          * Check if this (or a subsequent) instruction is related to
2369          * CONFIG_UBSAN or CONFIG_KASAN.
2370          *
2371          * End the search at 5 instructions to avoid going into the weeds.
2372          */
2373         if (!insn->func)
2374                 return false;
2375         for (i = 0; i < 5; i++) {
2376
2377                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2378                         return true;
2379
2380                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2381                         if (insn->jump_dest &&
2382                             insn->jump_dest->func == insn->func) {
2383                                 insn = insn->jump_dest;
2384                                 continue;
2385                         }
2386
2387                         break;
2388                 }
2389
2390                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2391                         break;
2392
2393                 insn = list_next_entry(insn, list);
2394         }
2395
2396         return false;
2397 }
2398
2399 static int validate_section(struct objtool_file *file, struct section *sec)
2400 {
2401         struct symbol *func;
2402         struct instruction *insn;
2403         struct insn_state state;
2404         int ret, warnings = 0;
2405
2406         clear_insn_state(&state);
2407
2408         state.cfa = initial_func_cfi.cfa;
2409         memcpy(&state.regs, &initial_func_cfi.regs,
2410                CFI_NUM_REGS * sizeof(struct cfi_reg));
2411         state.stack_size = initial_func_cfi.cfa.offset;
2412
2413         list_for_each_entry(func, &sec->symbol_list, list) {
2414                 if (func->type != STT_FUNC)
2415                         continue;
2416
2417                 if (!func->len) {
2418                         WARN("%s() is missing an ELF size annotation",
2419                              func->name);
2420                         warnings++;
2421                 }
2422
2423                 if (func->pfunc != func || func->alias != func)
2424                         continue;
2425
2426                 insn = find_insn(file, sec, func->offset);
2427                 if (!insn || insn->ignore || insn->visited)
2428                         continue;
2429
2430                 state.uaccess = func->uaccess_safe;
2431
2432                 ret = validate_branch(file, func, insn, state);
2433                 if (ret && backtrace)
2434                         BT_FUNC("<=== (func)", insn);
2435                 warnings += ret;
2436         }
2437
2438         return warnings;
2439 }
2440
2441 static int validate_functions(struct objtool_file *file)
2442 {
2443         struct section *sec;
2444         int warnings = 0;
2445
2446         for_each_sec(file, sec)
2447                 warnings += validate_section(file, sec);
2448
2449         return warnings;
2450 }
2451
2452 static int validate_reachable_instructions(struct objtool_file *file)
2453 {
2454         struct instruction *insn;
2455
2456         if (file->ignore_unreachables)
2457                 return 0;
2458
2459         for_each_insn(file, insn) {
2460                 if (insn->visited || ignore_unreachable_insn(insn))
2461                         continue;
2462
2463                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2464                 return 1;
2465         }
2466
2467         return 0;
2468 }
2469
2470 static struct objtool_file file;
2471
2472 int check(const char *_objname, bool orc)
2473 {
2474         int ret, warnings = 0;
2475
2476         objname = _objname;
2477
2478         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2479         if (!file.elf)
2480                 return 1;
2481
2482         INIT_LIST_HEAD(&file.insn_list);
2483         hash_init(file.insn_hash);
2484         file.c_file = find_section_by_name(file.elf, ".comment");
2485         file.ignore_unreachables = no_unreachable;
2486         file.hints = false;
2487
2488         arch_initial_func_cfi_state(&initial_func_cfi);
2489
2490         ret = decode_sections(&file);
2491         if (ret < 0)
2492                 goto out;
2493         warnings += ret;
2494
2495         if (list_empty(&file.insn_list))
2496                 goto out;
2497
2498         if (retpoline) {
2499                 ret = validate_retpoline(&file);
2500                 if (ret < 0)
2501                         return ret;
2502                 warnings += ret;
2503         }
2504
2505         ret = validate_functions(&file);
2506         if (ret < 0)
2507                 goto out;
2508         warnings += ret;
2509
2510         ret = validate_unwind_hints(&file);
2511         if (ret < 0)
2512                 goto out;
2513         warnings += ret;
2514
2515         if (!warnings) {
2516                 ret = validate_reachable_instructions(&file);
2517                 if (ret < 0)
2518                         goto out;
2519                 warnings += ret;
2520         }
2521
2522         if (orc) {
2523                 ret = create_orc(&file);
2524                 if (ret < 0)
2525                         goto out;
2526
2527                 ret = create_orc_sections(&file);
2528                 if (ret < 0)
2529                         goto out;
2530
2531                 ret = elf_write(file.elf);
2532                 if (ret < 0)
2533                         goto out;
2534         }
2535
2536 out:
2537         if (ret < 0) {
2538                 /*
2539                  *  Fatal error.  The binary is corrupt or otherwise broken in
2540                  *  some way, or objtool itself is broken.  Fail the kernel
2541                  *  build.
2542                  */
2543                 return ret;
2544         }
2545
2546         return 0;
2547 }